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BOSTON — Over the last 20 years, crime rates in the United States
have plunged precipitously — and mysteriously.

Far from taking credit for the decline, criminologists have been
scratching their heads over the reason for the drop in robberies,
assaults and burglaries. But new research points to a combination
of many small changes in recent decades, as well as the largely
ignored contributions of private crime prevention efforts, as
responsible.

"Over the course of a generation, we have had this extraordinary
change
in the crime picture," criminologist Philip J. Cook of Duke
University said here Saturday (Feb. 16) at the annual meeting of
the American Association for the Advancement of Science. "It is a
mystery, because no criminologist can say with any confidence
that they understand what's going on."

Cook and his colleagues studied the role of private security
efforts in tackling the problem of crime.

"There are more private security guards than there are police in
this country," Cook said. "I believe that private action, though
it has been largely ignored, deserves part of the credit."

One reason for a recent increase in the number of private
security guards is the rise of "business improvement districts" —
nonprofit organizations of businesses that tax themselves to pay
for extra measures to make their districts cleaner and safer,
including private security guards and surveillance.

Cook and his colleagues studied 30 business improvement districts
in Los Angeles between 1997 and 2008, and found that their
efforts caused an average of 28 fewer serious crimes per
neighborhood, which represents an 11 percent drop in
crime in those neighborhoods.

The scientists looked at how much money was being put toward
security in these districts, and they found that for every
$10,000 spent, the average number of crimes per neighborhood went
down by 3.4, meaning that business improvement districts that
spend more money on private security see a greater reduction in
crime. [ Q&A:
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"The bottom line here is we have a
reduction in crime — a reduction that is closely associated
with the expenditure of private security money," Cook said. "It
seems like a terrific accomplishment."

Cook was quick to point out, though, that these effects were just
a small part of the overall recent trends. He also pointed to
other small-scale changes, such as the increased use of credit
cards over cash, and the advent of immobilizer technology in cars
that prevents their engines from running without the correct
keys, as bearing some of the responsibility.

Another criminologist, Peter Reuter of the University of
Maryland, who was not involved in Cook's research, said he agreed
that private security efforts have played a role. He pointed to
the rise of gated communities, and technology advances that
prevent stolen cellphones from being reprogrammed, as additional
factors in
reducing crime.

Stop, Look and Listen

Jens Ludwig, director of the University of Chicago's Crime Lab,
studied another small-scale project that could pay significant
dividends in crime reduction.

Ludwig and his colleagues tested out a program called Stop, Look
and Listen at a Chicago juvenile detention center. The program
trained staff at the center to teach kids tactics used in
cognitive behavioral therapy (CBT), a psychological treatment
system that can help people override automatic behaviors, such as
reacting
violently. [ The
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"Part of crime is automatic behavior," Ludwig said. "In principle
we can make a little bit of a dent in the problem if we can make
kids slow down a little bit and act less automatically."

Though the program was relatively inexpensive, and not what
Ludwig called "gold standard CBT" — after all, it wasn't trained
psychologists working with the kids, but minimally trained
detention center staff — it made a difference.

The researchers found that juvenile offenders at the center who
were randomly assigned to the Stop, Look and Listen program were
less likely to become repeat offenders than kids who weren't.
Overall, the program reduced return rates to juvenile detention
by about 5 percent.

"The costs of crime are so huge that you don't need to make very
big changes in the problem to generate large dollar values,"
Ludwig said. "Social cost to society per homicide is on the order
of $10 million. The marginal cost of the intervention is
essentially just training the staff. We estimate the cost per kid
is $100 to $150, in exchange for a 5 percent reduction in return
rates to the facility."

Reuter, who was not involved in this study either, said it showed
promising results.

"It turns out that short interventions can make a difference," he
said.

Editor's Note: This story was updated to correct an error in
identifying the criminologist Peter Reuter, who was originally
identified as his co-author, Eric Sevigny of the University of
South Carolina.